Identifying and treating lung tissue abnormalities presents challenges that are somewhat unique to the lungs. If a tissue lesion or tumor is to be identified and excised surgically, the chest wall must be opened to provide access to the lungs. Opening the chest wall is a common procedure but one that presents risks of infection and lengthy recovery time, nonetheless.
A desirable alternative to surgery, in terms of reducing patient trauma, is to identify and excise the tumor endoscopically. Endoscopic surgery in the lungs, however, means that the complicated bronchial maze must be navigated. In order to assist in navigating the lungs, systems, such as that described in U.S. Pat. No. 7,233,820 to Gilboa, have been developed that include a sensor at the end of an endoscope.
The sensor is able to detect a plurality of magnetic fields generated by a location board, a flat mat on which the patient lies during the procedure. The magnetic fields collectively create an operable space known as a sensing volume. Each of the fields is oriented differently, such that three-dimensional coordinates of a sensor in the sensing volume can be determined and displayed. In order to overcome static interference such as the operating bed conducting parts, a mapping phase is performed when the system is installed. This mapping phase measures the actual shape of the magnetic field and generates correction or compensation parameters that enable the system to calculate the location of the sensor accurately taking into account the distorted magnetic field due to the static conducting parts.
Understandably, in order to provide useful, accurate data from within a body cavity, the sensor or sensors at the tip of the endoscope are very sensitive. Hence, if the magnetic field in the sensing volume is altered at all from the original field that was mapped during installation, such as by introduction of additional conducting objects into the sensing volume or changes to the previously mapped bed configuration the sensor will give data that is correspondingly altered. The result will be a sensor location indication that does not reflect the true location of the sensor. To the physician performing the procedure, it may not be evident that the magnetic field is being interfered with or that the sensor location indication is inaccurate.
It is evident that there is a need for a system and method of alerting a physician or other user of an endoscopic navigation system, such as that described above, that the magnetic field or data received has been compromised.